This project, as well as project number Z01-CP-04852-03-LVC, studies the biochemical and biophysical properties of nucleic acids and polypeptides of mammalian leukemia and sarcoma viruses. Our major findings are: 1. Poly(C) and poly(G) sequences are present in the RNA of retroviruses from avian to primate isolates. 2. Little or no poly(C) and poly(G) sequences are present in the nucleic acids examined from nonmalignant mammalian and human embryonic cells. 3. The poly(C) and poly(G) sequences in the RNA of retroviruses are transcribed into poly(dG) and poly(dC) tracts respectively in the subunit-length viral cDNA. 4. Genomic and subunit RNA of mammalian leukemia and sarcoma viruses have regions of double-stranded RNA. 5. Gazdar murine sarcoma virus (Gz-MSV) and Moloney murine sarcoma virus (M-MSV) are closely related and possibly Gz-MSV is a variant of M-MSV as determined by nucleic acid hybridization studies and analysis of viral expression in cells. 6. These studies represent a possible molecular approach to cancer therapy for some types of viral neoplasia, especially human leukemia and cancer of the breast.